A group of grass frogs sleeping upside down on a leaf showing camouflage.
Jesse Delia
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Jesse Delia
A group of grass frogs sleeping upside down on a leaf showing camouflage.
Jesse Delia
Jesse Delia says it happened in Panama. A few years ago he had finished his fieldwork. A research project investigating parental behavior of a species of grass frog. He brought several half-dollar-sized transparent frogs into the lab for photography.
It led to an interesting discovery.
“I wanted to take a cute glass frog belly picture,” Delia told NPR. He placed them in Petri dishes and saw each frog’s circulatory system through its translucent skin, or “red with red blood cells.”
However, when he returned later, the frog was asleep and the blood was “gone”.
It was as if arteries and veins had melted. “I thought it was crazy,” recalls Delia, now a biologist at the American Museum of Natural History in New York.
He videotaped the glass frog’s heartbeat and sent it to longtime collaborator Carlos Taboada, a biologist at Duke University.
“It was colorless,” says Taboada. I couldn’t even see the red streak of the container on the frog’s belly. “I was insane. I had never seen anything like that before.”
Both Delia and Taboada wanted to know—where did all the frog red blood go?
of new paper in the journal chemistryTaboada, Delia, and their collaborators respond, “They hide most of their red blood cells in the liver.”
The same grass frog photographed during sleep (left) and activity (right) shows differences in red blood cell circulation.
Jesse Delia
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Jesse Delia
The same grass frog photographed during sleep (left) and activity (right) shows differences in red blood cell circulation.
Jesse Delia
During the day, while sleeping on green leaves, glass frogs are vulnerable to predators, so they become ultra-transparent for camouflage. (The liver, among other organs, is covered in highly reflective white crystals.) Frog red blood cells transport very little oxygen, which is why Delia says frogs “keep cells alive while they’re transparent.” It is likely that they have some alternative process that allows them to leave. Then, at night, when the frogs become active, “foraging and mating, and doing their normal work,” the vitreous amphibians put red blood cells back into circulation.
Frogs “pack about 90% of their red blood cells into a very small volume, and usually these conditions can lead to some clotting problems,” says Taboada. Researchers say knowing how glass frogs circumvent the blood clotting cascade could pave the way for new anticoagulants for humans.
